After the 1993 outbreak of illness caused by Cryptosporidium in Milwaukee, the city moved forward on an $89 million upgrade of its treatment facilities with ozone filtration, the only disinfectant technology that kills Cryptosporidium. Providing safe drinking water is a quietly important issue for every city. However, in March 1993 the issue came front and center for the city of Milwaukee when Cryptosporidium—a microorganism that causes gastrointestinal illness in humans—contaminated the city drinking water, affecting an estimated 400,000 people. For some people with immune-system deficiencies, Cryptosporidiosis proved fatal. To ensure this situation would not recur, the city of Milwaukee launched a comprehensive program to upgrade the Milwaukee Water Works facilities and provide safer drinking water.